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Modeling Gale Crater

Recently, news came out of NASA’s Jet Propulsion Laboratory which stated that using data and imagery from the Curiosity rover, they were able to prove that Gale Crater (in which Curiosity currently resides) used to contain a body of liquid water. These findings also show that in the distant past, and given the liquid water, Mars may have been able to support microbial life. I am certainly not a scientist so my understanding is limited, but this does seem to be great news for the possibility of life beyond Earth.

Now, I’m not one to sit idly by while news like this breaks.
There’s not much I can do; I can’t go to Mars and personally validate the results (as much as I’d like to), and I don’t consider myself a particularly good science writer so I’ll leave that task to the experts. So what’s in my wheelhouse? Software or graphics. I’m not about to code some water on Mars, so I chose the graphics route.

Despite some really nice computer graphics floating around the web of Gale Crater, I found that actually obtaining the data wasn’t exactly obvious. I’ll spare you the boring details of me searching around and go straight to the findings… As it turns out, the best altimetry data for Gale is derived from the High Resolution Stereo Camera (HRSC) onboard the European Space Agency’s Mars Express orbiter. I read the article “Geologic mapping and characterization of Gale Crater and implications for its potential as a Mars Science Laboratory landing site (Anderson, Bell)”, and was able to derive the features of the crater along with the corresponding orbital passes of the spacecraft (1916, 1927, 1938) so as to retrieve the relevant data from NASA’s Planetary Data System. The free and capable tool “FITS Liberator” was able to process the raw data into usable images that I could bring into Photoshop. The altimetry and visual data were aligned and merged in a rather unscientific manner (I overlayed and blended the overlapping data) so as to avoid the seams between the data strips that appears in a lot of Gale models. Some brightness corrections were also made to calibrate and normalize the data. Because the visual imagery is in grayscale, I performed a best-effort colorization. For distant terrain, and since Gale imagery only spans the area of the crater and it’s immediate surroundings, I pulled in some Viking imagery to extend out to the horizon. I converted that to grayscale and recolorized it to match the Mars Express images. I got close(ish) with matching the color, but optimal camera angles and focus blurring in the model somewhat hides the difference.

Creating the model in Maya was a little bit of trial and error. Before all this, I had attempted to use the 3D printable mesh of Gale from NASA’s 3D resources page, but that proved a bit unwieldy for texturing and UV mapping in Maya. The Mars Express data (on which NASA’s model is also based) was great for creating shading and vertex displacement, but that also quickly hogged all sixteen gigs of RAM my laptop has and made for super-long render times. The answer I found was to use the “Displacement to Polys” tool in Maya and then run a face reduction to cut down the number of resultant polygons as bump mapping would nicely handle the finer details. The water was a simple plane mesh using the ocean shader, though I mapped the ocean texture to the displacement node and used it to again update the polys (faster render, better reflections). Adding a physical sun and sky node rounded the model out quite nicely. Post rendering adjustments in Photoshop to sharpen, add the clouds and solar glare finished the product.

Below are the digital assets I came up with the produce the model. I’m not including the Maya project mainly because (its mine) I’d more like to see what other people can come up with these resources.